Electronic power amplifying technology and digital optical disk recording technology of the recent years are providing high fidelity audio signals. Thus in any sound system ultimate quality depends on the speakers. The best recording, encoded on the most advanced storage device and played by a top-of-the-line deck and amplifier, can have a quality sound only if the system is hooked up to high quality speakers. A system's speaker is the component that takes the electronic signal stored on equipment like CDs tapes and DVDs and converts them into actual sound that we can hear.
The loudspeaker is a transducer converting electrical drive signal into sound waves. The core element of the transducer is the driver, which produces sound waves by rapidly vibrating a flexible cone, or diaphragm. The cone, usually made of paper, plastic or metal, is attached on the wide end to the suspension, a rim of flexible material that allows the cone to move, and is attached to the driver's metal frame.
The narrow end of the cone is connected to the voice coil, an electromagnet commonly made of electrical wire windings around a core of magnetic material and placed in the center of a permanent magnet ring. An electrical current running through the wire creates a varying magnetic field around the coil, interacting with the permanent magnet ring to apply force directed along the cone axis to move the voice coil freely back and forth along the cone axis.
Physical size of this audio transducer technique, limit the frequency range that a given driver can output. A large and heavy voice coil adapted for operating accurately at low audio frequencies, operates poorly for the higher audio frequencies and vice versa, a small and light voice coil adapted for operating accurately at high audio frequencies, operates poorly for the lower audio frequencies. Thus, three independent drivers, commonly produce the entire sound spectral range from the lowest sound wave frequencies up to the highest audible frequency of approximately 20 KHz. Woofers are the biggest drivers, and are designed to produce low frequency sounds. Midrange drivers produce a range of frequencies in the middle of the sound spectrum. Tweeters are the units, designed to produce the highest frequencies. Consequently, The input to each driver contains the spectral components of the audio signal, which are compatible with the driver operational frequency by having a device known in the art by the name: crossover. The crossover includes a low pass filter, a band pass filter and a high pass filter. The input to the crossover is an audio voltage driven by the output of the audio power amplifier. The output of the low pass filter is used to drive the voice coil of the woofer. The output of the band pass filter is used to drive the voice coil of the mid range driver and the output of the high pass filter is used to drive the tweeter. The sound created by the three transducers effectively combines the three spectral ranges into a single consecutive audible spectral range.
Commonly, a loudspeaker system is constructed by a single common housing structure including the crossover filter and the three independent drivers. Consequently, a high quality loudspeaker has a large physical size. Furthermore, this loudspeaker configuration is highly sensitive to tuning between the three voice coil drivers and the corresponding crossover output voltages, resulting performance degradation. In view of the fact that loudspeakers are the ‘weak link’ of an audio system, systems and methods were devised in the past years for improving the sound fidelity of loudspeakers.
U.S. Pat. No. 4,283,606 enclosed herein by reference discloses an acoustic filter for use in combination with a coaxial loudspeaker system, which includes a low frequency loudspeaker and a high frequency loudspeaker, which is axially aligned with the low frequency loudspeaker. The acoustic filter includes a pair of parallel, perforated sheets which are separated from each other a suitable distance and which are joined together at their peripheries in any appropriate manner so that they enclose an airspace there between in order to form a single section filter. The acoustic filter is disposed between the low frequency loudspeaker and the high frequency loudspeaker so the acoustic filter inhibits the high frequency sounds of the high frequency loudspeaker from interacting with the internal sidewall of the conically shaped diaphragm of the low frequency loudspeaker.
U.S. Pat. No. 4,357,498 enclosed herein by reference discloses a coaxial type planar diaphragm loudspeaker system in which a plurality of coaxially arranged polygonal diaphragms are provided with separate magnetic circuits. Each magnetic circuit includes two parallel plate along each side of the diaphragm with a voice coil bobbin having the same shape as the corresponding polygonal diaphragm coupled thereto with a voice coil attached to the opposite end and disposed in the gap formed in the magnetic circuit. The area of the diaphragm falling within the juncture line between the voice coil bobbin and diaphragm is made equal to the area of the diaphragm outside the juncture line so as to eliminate split vibration.
U.S. Pat. No. 5,193,119 enclosed herein by reference discloses a multiple loudspeaker includes a housing and a first speaker (a woofer) supported by the housing. The first speaker includes a first diaphragm. A support for supporting a second speaker (a tweeter) is provided, and the housing supports the tweeter support. A portion of the support for the tweeter is spaced from the first diaphragm (the woofer diaphragm), and the tweeter is spaced from the woofer diaphragm. The tweeter support can be in the form of a protective grill or in the form of an annular ring. A sponge damper is attached to the spaced portion of the tweeter support. The tweeter includes a second diaphragm (the diaphragm for the tweeter) and a piezoelectric transducer. The tweeter diaphragm is attached to and is supported by the sponge damper. The piezoelectric transducer is attached to and supported by the tweeter diaphragm and is spaced from the woofer diaphragm. The piezoelectric transducer faces and is spaced from the woofer without an obstruction being present between the piezoelectric transducer and the woofer diagram. The surface of the woofer diaphragm reflects the sound waves emitted from the rear of the piezoelectric transducer and the rear of the tweeter diaphragm.
U.S. patent application Ser. No. 11/450,900 enclosed herein by reference discloses a loudspeaker is provided for receiving an electrical signal and transmitting an acoustic signal through a transmission medium. The system includes generally two elements: a coaxial transducer and an acoustic transformer. The coaxial transducer includes a high-frequency driver and a mid-frequency driver that are coaxially arranged. The acoustic transformer is acoustically coupled to the coaxial transducer and includes an initial horn section that expands from a first end to a second end in a direction away from the coaxial transducer. The initial horn section defines a plurality of openings there through, such that the initial horn section is acoustically opaque to high-frequency acoustic signals to thereby function as a wave-guide for the high-frequency acoustic signals, while it is acoustically transparent to mid-frequency acoustic signals.
Hence there is still a long felt need for a compact and high sound quality loudspeaker system that is insensitive to audio filter tuning variations with respect to transducer spectral response curves.